[jira] [Created] (FLINK-5479) Per-partition watermarks in FlinkKafkaConsumer should consider idle partitions

[Shang Yuanchun (Jira)]

Tzu-Li (Gordon) Tai created FLINK-5479:
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             Summary: Per-partition watermarks in FlinkKafkaConsumer should consider idle partitions
                 Key: FLINK-5479
                 URL: https://issues.apache.org/jira/browse/FLINK-5479
             Project: Flink
          Issue Type: Improvement
          Components: Kafka Connector
            Reporter: Tzu-Li (Gordon) Tai
             Fix For: 1.3.0


Reported in ML: http://apache-flink-user-mailing-list-archive.2336050.n4.nabble.com/Kafka-topic-partition-skewness-causes-watermark-not-being-emitted-td11008.html

Similar to what's happening to idle sources blocking watermark progression in downstream operators (see FLINK-5017), the per-partition watermark mechanism in `FlinkKafkaConsumer` is also being blocked of progressing watermarks when a partition is idle. The watermark of idle partitions is always `Long.MIN_VALUE`, therefore the overall min watermark across all partitions of a consumer subtask will never proceed.

It's normally not a common case to have Kafka partitions not producing any data, but it'll probably be good to handle this as well. I think we should have a localized solution similar to FLINK-5017 for the per-partition watermarks in `AbstractFetcher`.



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